linux-kernel - Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c

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Message-ID: <48B5F9F3.20505@snapgear.com>
Date:	Thu, 28 Aug 2008 11:05:55 +1000
From:	Greg Ungerer <gerg@...pgear.com>
To:	Paul Mundt <lethal@...ux-sh.org>, Adrian Bunk <bunk@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Alan D. Brunelle" <Alan.Brunelle@...com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, linux-embedded@...r.kernel.org
Subject: Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected


Paul Mundt wrote:
> On Wed, Aug 27, 2008 at 02:58:30PM +0300, Adrian Bunk wrote:
>> On Tue, Aug 26, 2008 at 05:28:37PM -0700, Linus Torvalds wrote:
>>> On Wed, 27 Aug 2008, Adrian Bunk wrote:
>>>> When did we get callpaths like like nfs+xfs+md+scsi reliably 
>>>> working with 4kB stacks on x86-32?
>>> XFS may never have been usable, but the rest, sure.
>>>
>>> And you seem to be making this whole argument an excuse to SUCK, adn an 
>>> excuse to let gcc crap even more on our stack space.
>>>
>>> Why?
>>>
>>> Why aren't you saying that we should be able to do better? Instead, you 
>>> seem to asking us to do even worse than we do now?
>> My main point is:
>> - getting 4kB stacks working reliably is a hard task
>> - having an eye on gcc increasing the stack usage, and fixing it if
>>   required, is relatively easy
>>
>> If we should be able to do better at getting (and keeping) 4kB stacks 
>> working, then coping with possible inlining problems caused by gcc
>> should not be a big problem for us.
>>
> Out of the architectures you've mentioned for 4k stacks, they also tend
> to do IRQ stacks, which is something you seem to have overlooked.
> 
> In addition to that, debugging the runaway stack users on 4k tends to be
> easier anyways since you end up blowing the stack a lot sooner. On sh
> we've had pretty good luck with it, though most of our users are using
> fairly deterministic workloads and continually profiling the footprint.
> Anything that runs away or uses an insane amount of stack space needs to
> be fixed well before that anyways, so catching it sooner is always
> preferable. I imagine the same case is true for m68knommu (even sans IRQ
> stacks).

Yep, definitely true for m68knommu in my experience. I haven't had
any problems with 4k stacks recently. But yes the workloads do tend
to be constrained - and almost never use any of the more exotic
filesystems or drivers.



> Things might be more sensitive on x86, but it's certainly not something
> that's a huge problem for the various embedded platforms to wire up,
> whether they want to go the IRQ stack route or not.
> 
> In any event, lack of support for something on embedded architectures in
> the kernel is more often due to apathy/utter indifference on the part of
> the architecture maintainer rather than being indicative of any intrinsic
> difficulty in supporting the thing in question. Most new "features" on the
> lesser maintained architectures tend to end up there either out of peer
> pressure or copying-and-pasting accidents rather than any sort of design.
> ;-)

Indeed :-)

Regards
Greg


------------------------------------------------------------------------
Greg Ungerer  --  Chief Software Dude       EMAIL:     gerg@...pgear.com
Secure Computing Corporation                PHONE:       +61 7 3435 2888
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